package com.sky.utils;

import com.sky.properties.SnowflakeIdWorkerProperties;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;

import java.net.InetAddress;
import java.net.NetworkInterface;

@Component
public class SnowflakeIdWorkerUtil {

    // ==============================Fields========================================
    /** 开始时间截 (2020-01-01) */
    private final long twepoch = 1577836800000L;
    /** 机器id所占的位数 */
    private final long workerIdBits = 5L;
    /** 数据标识id所占的位数 */
    private final long datacenterIdBits = 5L;
    /** 支持的最大机器id，结果是31 (5位二进制整数最大是31) */
    private final long maxWorkerId = -1L ^ (-1L << workerIdBits);
    /** 支持的最大数据标识id，结果是31 */
    private final long maxDatacenterId = -1L ^ (-1L << datacenterIdBits);
    /** 序列在id中占的位数 */
    private final long sequenceBits = 12L;
    /** 机器ID向左移12位 */
    private final long workerIdShift = sequenceBits;
    /** 数据标识id向左移17位(12+5) */
    private final long datacenterIdShift = sequenceBits + workerIdBits;
    /** 时间截向左移22位(5+5+12) */
    private final long timestampLeftShift = sequenceBits + workerIdBits + datacenterIdBits;
    /** 生成序列的掩码，这里为4095 (0b111111111111=0xfff=4095) */
    private final long sequenceMask = -1L ^ (-1L << sequenceBits);

    /** 工作机器ID(0~31) */
    private long workerId;
    /** 数据中心ID(0~31) */
    private long datacenterId;
    /** 毫秒内序列(0~4095) */
    private long sequence = 0L;
    /** 上次生成ID的时间截 */
    private long lastTimestamp = -1L;

    // ==============================Constructors=====================================
    public SnowflakeIdWorkerUtil(SnowflakeIdWorkerProperties snowflakeIdWorkerProperties) {
        this.workerId = snowflakeIdWorkerProperties.getWorkerId();
        this.datacenterId = snowflakeIdWorkerProperties.getDataCenterId();

        // 检查ID是否合法
        if (this.workerId > maxWorkerId || this.workerId < 0) {
            throw new IllegalArgumentException(String.format("worker Id can't be greater than %d or less than 0", maxWorkerId));
        }
        if (this.datacenterId > maxDatacenterId || this.datacenterId < 0) {
            throw new IllegalArgumentException(String.format("datacenter Id can't be greater than %d or less than 0", maxDatacenterId));
        }
    }

    // ==============================Methods==========================================
    /**
     * 获得下一个ID (该方法是线程安全的)
     */
    public synchronized long nextId() {
        long timestamp = timeGen();

        // 如果当前时间小于上一次ID生成的时间戳，说明系统时钟回拨过，这时候应当抛出异常
        if (timestamp < lastTimestamp) {
            throw new RuntimeException(String.format("Clock moved backwards.  Refusing to generate id for %d milliseconds", lastTimestamp - timestamp));
        }

        // 如果是同一时间生成的，则进行毫秒内序列
        if (lastTimestamp == timestamp) {
            sequence = (sequence + 1) & sequenceMask;
            // 毫秒内序列溢出
            if (sequence == 0) {
                // 阻塞到下一个毫秒,获得新的时间戳
                timestamp = tilNextMillis(lastTimestamp);
            }
        } else {
            // 时间戳改变，毫秒内序列重置
            sequence = 0L;
        }

        // 上次生成ID的时间截
        lastTimestamp = timestamp;

        // 移位并通过或运算拼到一起组成64位的ID
        return ((timestamp - twepoch) << timestampLeftShift) |
                (datacenterId << datacenterIdShift) |
                (workerId << workerIdShift) |
                sequence;
    }

    /**
     * 阻塞到下一个毫秒，直到获得新的时间戳
     */
    protected long tilNextMillis(long lastTimestamp) {
        long timestamp = timeGen();
        while (timestamp <= lastTimestamp) {
            timestamp = timeGen();
        }
        return timestamp;
    }

    /**
     * 返回以毫秒为单位的当前时间
     */
    protected long timeGen() {
        return System.currentTimeMillis();
    }

    // 主机地址和端口信息获取
    public static long getWorkerId() {
        long workerId = 0L;
        try {
            InetAddress ip = InetAddress.getLocalHost();
            NetworkInterface network = NetworkInterface.getByInetAddress(ip);
            if (network == null) {
                workerId = 1L;
            } else {
                byte[] mac = network.getHardwareAddress();
                long macAddrHigh = 0L;
                long macAddrLow = 0L;
                if (null != mac) {
                    for (int i = 0; i < mac.length; i++) {
                        if (i == 0) {
                            macAddrHigh |= (0x000000FF & (long) mac[i]) << (8 * (mac.length - 1 - i));
                        } else {
                            macAddrLow |= (0x000000FF & (long) mac[i]) << (8 * (i - 1));
                        }
                    }
                }
                workerId = (macAddrHigh << 16 | macAddrLow) & 0x0000FFFF;
            }
        } catch (Exception e) {
            workerId = 1L;
        }
        return workerId;
    }

}